Advise ? Am I wrong.

I have a 6 year old. My sons father and I separated about 2 years ago .. He had another child and stayed with the girl.. Ok . I myself have moved on and in a wonderful relationship. My little boy literally calls his dad everyday.. And not once does he answer.. He picks him up once a week.. I do have him on child support pays every month that's no problem. My son has been acting up a lot... For attention. I'm wondering if him not seeing his dad a lot could be 1 reason? Since his dad lives with his little brother .. I'm getting just a little frustrated because the first week of school .. My son was not doing well at all, always getting red smiley faces, teacher told me he hit a kid, wouldn't listen.. I had a talk with my son and he tells me the kids are making fun of him calling him skinny bla bla.. I reached out to his father.. To keep him in the loop ( which I always do right away) but not one response.. I get he has his own problems with work, wife & child... But I would think that if your child is getting bullied you'd like to be in the loop.. I'm wondering if I should stop.. You know informing him... Anyone else going through this ?